Interference of Crx-dependent transcription by ataxin-7 involves interaction between the glutamine regions and requires the ataxin-7 carboxy-terminal region for nuclear localization

• Published in: Human molecular genetics Vol. 13; no. 1; pp. 53 - 67
• Main Authors: Chen, Shiming, Peng, Guang-Hua, Wang, Xuejiao, Smith, Annette C., Grote, Sara K., Sopher, Bryce L., La Spada, Albert R.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.01.2004; Oxford Publishing Limited (England)
• Subjects: Animals; Ataxin-7; beta-Galactosidase; Biological and medical sciences; Blotting, Western; Cell Nucleus - metabolism; Cells, Cultured; Classical genetics, quantitative genetics, hybrids; cone-rod dystrophy; Crx protein; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Disease Models, Animal; DNA Primers; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation; Genetic Vectors; Genetics of eukaryotes. Biological and molecular evolution; Glutamine - metabolism; Homeodomain Proteins - metabolism; Human; Immunohistochemistry; Luciferases; Medical sciences; Mice; Molecular and cellular biology; Molecular genetics; Mutagenesis; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Neurology; Photoreceptor Cells, Vertebrate - metabolism; Precipitin Tests; Protein Binding; Protein Structure, Tertiary; Retinal Degeneration - complications; Retinal Degeneration - genetics; Retinal Degeneration - metabolism; Spinocerebellar Ataxias - complications; Spinocerebellar Ataxias - genetics; Trans-Activators - metabolism; Transcription, Genetic - genetics; Transcription. Transcription factor. Splicing. Rna processing; Two-Hybrid System Techniques; Spinocerebellar heredodegeneration; Nervous system diseases; Transcription; Central nervous system disease; Interference; Genetics; Degenerative disease; Localization; Spinal cord disease; Cerebral disorder; Genetic disease; Glutamine
• ISSN: 0964-6906; 1460-2083; 1460-2083
• DOI: 10.1093/hmg/ddh005

Spinocerebellar ataxia type 7 (SCA7) is an inherited neurodegenerative disorder caused by expansion of a polyglutamine tract in the ataxin-7 protein. A unique feature of SCA7 is degeneration of photoreceptor cells in the retina, resulting in cone–rod dystrophy. In an SCA7 transgenic mouse model that we developed, it was found that the cone–rod dystrophy involves altered photoreceptor gene expression due to interference with Crx, a homeodomain transcription factor containing a glutamine-rich region. To determine the basis of the Crx–ataxin-7 interaction, Crx and ataxin-7 truncation and point mutants were generated, and the ability of mutant versions of either protein to co-immunoprecipitate the normal version of the other protein was tested. Thus Crx's ataxin-7 interaction domain was localized to its glutamine-rich region and ataxin-7's Crx binding domain was mapped to its glutamine tract. The importance of each protein's respective glutamine region for a productive interaction was confirmed by performing Crx transactivation assays in HEK293 cells and correlating the extent of Crx transcription interference with the intactness of each protein's glutamine region. It was also established that ataxin-7 must localize to the nucleus to repress Crx transactivation, and the likely nuclear localization signals were mapped to ataxin-7's carboxy-terminal region. Finally, using chromatin immunoprecipitation, it was demonstrated that Crx and ataxin-7 engage in a functionally significant interaction by co-occupying the promoter and enhancer regions of Crx-regulated retinal genes in vivo. The results suggest that one mechanism of SCA7 disease pathogenesis is transcription dysregulation, and that Crx transcription interference is a predominant factor in SCA7 cone–rod dystrophy retinal degeneration.